Pulverizing apparatus of various types has been used for decades to reduce the particle size of a variety of solid materials (e.g., coal). Pulverizing mills are commonly used in power generating plants to crush and grind coal to produce coal dust used as fuel in the generation of electrical power. Pulverizing mills of this type are described, for example, in U.S. Pat. Nos. 4,523,721, 4,264,041, and 4,687,145.
The pulverizing mills described in such patents include a housing, a rotating bowl member for crushing solid materials such as coal present in the bowl, and an annular passage between the interior surface of the housing and the periphery of the bowl member which enables air to flow upwardly through the passage. As the coal is crushed and made into small particles (i.e., dust), the air flowing upwardly through the passage at the periphery of the bowl is intended to lift and carry the dust particles out of the housing and into a fuel stream for the power plant.
The conventional throat/air port designs used in prior pulverizing mills require expensive and difficult installation techniques using wear-resistant materials. The vanes which are present in the throat are typically tilted at least about 45.degree. from vertical and are oriented in the direction of rotation of the rotating bowl member.
Prior designs are complicated. For adequate service life, all typically require the use of wear-resistant material which is quite heavy. Some designs utilize a series of stationary throats or vanes and some utilize rotatable throats.
All conventional throat/air port designs are intended to swirl the upwardly moving air or cause it to spin as it passes through the throat area. This requires rapidly moving air. Such swirling air, however, creates an unnecessary turbulence inside the mill body. This turbulence or swirling air flow will cause local high rates of wear on all internal mill parts. This is due to the nature of the prior designs and their continual contact with pulverized coal particles.